These studies have employed antibodies to carcinogen-DNA adducts to investigate the extent and nature of binding of 2-acetylaminofluorene (2-AAF) and benzo(a) pyrene (BP) in DNA in vivo and in vitro. By radioimmunoassay it is possible to quantitate and distinquish between the acetylated and deacetylated C-8 adducts of 2-AAF. In vitro studies with this assay have concentrated on determining and manipulating the adducts formed in the DNA of cultured cells upon exposure to N-acetoxy-2-acetylaminofluorene. The nature and extent of binding has also been monitored in the livers and kidneys of male rats fed a carcinogenic dose of 2-AAF for up to 16 weeks. Antisera raised against BP bound to deoxyguanine in DNA have been utilized in ELISA and USERIA assays to detect less than 1 femtomole of BPdG adducts, and human tissues from individuals exposed environmentally or occupationally to polycyclic aromatic hydrocarbons are being screened for the presence of adducts on DNA. The BP-DNA antisera have also been used for the visualization of BP adducts on calf thymus DNA by electron microscopy and in nuclei of BP-exposed cultured cells by immunofluorescence.